CN101340417A - Improved iterative PTS method for lowering peak-average-ratio in OFDM system - Google Patents

Abstract

The invention relates to an improved iterative PTS method for reducing peak-to-average power ratio in an OFDM system, and the technical proposal is as follows: an improved iterative PTS algorithm is proposed by using an OFDM system model under a frequency selective fading channel, taking the reduction of the complexity of the traditional algorithm as a starting point and taking the traditional partial transfer sequence method PTS for reducing the peak-to-average power ratio (PAPR) as the basis. The improved iterative PTS method is characterized by comprising the following steps: a frame of input OFDM symbols is segmented into V subsequences which are not overlapped mutually, the minimum PAPR is calculated by summing various sub-blocks, sideband information is integrated and the combination with the minimum PAPR is selected for sending. The method can ensure the applicability of a wireless communication system under a wireless fading channel and reduce the PAPR of the OFDM system without the increase of the complexity of the system, thereby realizing balance between the applicability of the system and the complexity of the system, having no need of sending the sideband information additionally and improving the reliability of the system and the availability of the system.

Description

Modified model reduces the iterative PTS method of peak-to-average force ratio in the ofdm system

Technical field

The present invention relates to wireless communication technology field, be meant the iterative PTS method of modified model reduction peak-to-average force ratio in a kind of ofdm system especially.Can be applicable to the design of ofdm system reduction peak-to-average force ratio.In constantly the improving of next generation wireless communication system,, existing OFDM wireless communication system reduces based on traditional partial transmission sequence method (PTS) that peak-to-average power carries out improved iterative PTS new method than (PAPR) and communication is reliably supported for providing a kind of.Have characteristics such as low complex degree, accuracy.

Background technology

Demand broadband to communicating by letter along with people, individualized and mobile is more and more higher, and OFDM (OFDM) technology has obtained using widely at each wireless communication field.One big shortcoming of ofdm system is that higher peak-to-average power ratio is arranged, the transmission signal of ofdm system is superimposed the forming of transmission signal on a plurality of subcarriers, when these signals during with the addition of homophase phase place, the instantaneous power of gained signal is very big, the average power of signal causes system to produce higher PAPR head and shoulders above.High PAPR has proposed very high requirement to the range of linearity of the power amplifier in the transmitter and receiver, and has increased the complexity of equipment such as A/D, D/A converter.If the range of linearity of amplifier can not satisfy the dynamic change scope of signal, then signal can produce nonlinear distortion, causes spectrum leakage, and the orthogonality between each subcarrier is destroyed, and produces inter-carrier interference, reduces the performance of system.So peak-to-average power is the major issue that ofdm system need solve than problem.

In the wireless OFDM system, the technology that reduces PAPR at present both at home and abroad mainly is divided into 3 classes: signal predistortion class technology, coding class technology, signal scrambling code class technology.The thought of signal predistortion class technology is that direct peak value to signal carries out nonlinear operation, and is the most direct, the simplest.Because what it adopted is nonlinear operation, produced outside in-band noise and the band and disturbed, so the error rate of system is than higher.The thought of coding class technology is only to send the code word that those have low PAPR characteristic, thereby has avoided sending the code word that those higher PAPR can occur.Such technology is a linear process, can not make signal produce distortion, does not therefore also have the shortcoming of amplitude limit class technology.But the computation complexity of coding class technology is very high, and encoding and decoding all bother very much, the more important thing is that the information rate of this class technology reduces very soon, therefore only are applicable to the situation that sub-carrier number is fewer.Signal scrambling code class technology, its core concept are to reduce the probability that big PAPR occurs, employing also be linear transformation, but such technical sophistication degree need carry out repeatedly IFFT computing and search procedure than higher.

Summary of the invention

The objective of the invention is to avoid above-mentioned weak point of the prior art and provide modified model in a kind of ofdm system to reduce the iterative PTS method of peak-to-average force ratio.A kind of method that guarantees the applicability of wireless communication system and do not increase the reduction ofdm system PAPR of system complexity under wireless fading channel is provided, can realize the applicability of system and the equilibrium between the system complexity, guarantee the application demand of real system, and need not other transmitted sideband information, further improve system reliability, improve the availability of system.

Purpose of the present invention can reach by following measure:

Modified model reduces the iterative PTS method of peak-to-average force ratio in a kind of ofdm system, ofdm system model under frequency selective fading channels, reduce at traditional partial transmission sequence method on the basis of peak-to-average power ratio, propose a kind of modified model iterative PTS algorithm, comprise the following steps: that the combination that the frame OFDM symbol segmentation that will import becomes subsequence, each sub-piece addition of V non-overlapping copies to ask minimum PAPR, integration side information and selection to have minimum PAPR sends;

Become the subsequence particular content of V non-overlapping copies to comprise a frame OFDM symbol segmentation of input: in comprising N sub-carrier OFDM system, transmitting data information is through the mapping of modulation systems such as QAM, data flow X _kCarry out obtaining the time domain OFDM symbol after the N point IFFT conversion, the subvector that at first a frame OFDM data vector to be sent is divided into V non-overlapping copies with the adjacent method of cutting apart, the length of each subvector is N/V, and then carrying out corresponding zero padding for each subvector after cutting apart becomes V partial transmission sequence X ^v, v=1,2 ..., V, V partial transmission sequence with gained carries out the IFFT conversion respectively then;

Each sub-piece addition asks minimum PAPR particular content to comprise: it is x that V partial transmission sequence carries out the time-domain signal that the IFFT conversion obtains ^v, v=1,2 ..., V makes x=x ¹+ x ²+ ...+x ^vCalculate the PAPR value of primary signal this moment, be designated as PAPR _Initial, and make PAPR _PTS=PAPR _Initial, PAPR wherein _PTSBe the minimum PAPR value of setting, introduce the phase rotation coefficient combination

b _vBe also referred to as side information (SI), remove weighting V sub-piece vector,, make that the PAPR value that merges the back sequence is minimum by selecting optimum phase rotation coefficient combination with phase rotation coefficient, the phase factor set select scope be ± 1, ± i}, and initialization b _v=1, v=1,2 ... V, initialization v=1 through the method for searching loop, finds out the b that makes the PAPR minimum _vValue;

Integrating the side information particular content comprises: in same OFDM symbol, adopt zero carrier to send side information few in number, data and side information send simultaneously, need not in addition transmitted sideband information separately, reduce the complexity of receiving terminal;

The combination that selection has a minimum PAPR sends particular content and comprises: utilize zero subcarrier structure to comprise the partial transmission sequence of side information, one of many structure are used for demodulation, here be fixed as 1, the residing position of side information is the position of zero carrier among the X, and its structural form is: P=[0,0, ..., 0,1, b ₁, b ₂..., b _V, 0,0 ... 0], the side information frequency-region signal P that is constructed is carried out the IFFT conversion, obtain time-domain signal p, under the situation of the time-domain signal x of the PAPR minimum that obtains in the above, calculate x ± p, the PAPR value of signal under four kinds of situations of x ± p*i, the combination of selecting to have minimum PAPR sends.

The present invention has following advantage compared to existing technology:

1. modified model iterative PTS algorithm is based on and carries out improvedly on traditional partial transmission sequence method, and what it carried out the OFDM symbol is linear transformation, and does not bring distortion and out-of-band radiation in any band.

2. this invention has significantly reduced the complexity of system, and traditional PTS method is having W through the phase combination mode after the IFFT ^VKind, and only need (V-1) W search procedure adopt this alternative manner after, so the system complexity of this iterative algorithm during much smaller than traversal search (general V 〉=W).The each several part transfer sequence need constantly superpose in the hope of the PAPR value in iterative process, if adopt every iteration once all to need the method for each subsequence stack, so total addition number of times is (V-1) (V-1) WN, but earlier each sub-piece is superposeed if adopt, each iterative search procedures is is only partly added and subtracted the partial transmission sequence of corresponding conversion, then amount of calculation will reduce, and needed like this addition number of times becomes (V-1) (W+1) N, has further reduced the complexity of system.

3. need not other transmitted sideband information, adopt zero carrier to send side information few in number, make data and side information in same OFDM symbol, send, reduced the complexity of receiving terminal.

Description of drawings

Fig. 1 is the transmitting-receiving block diagram that ofdm system of the present invention is suitable for.

Fig. 2 is the schematic diagram of the invention process partial transmission sequence method.

To be the invention process partial transmission sequence method count analogous diagram under the situation at the sub-piece of difference to Fig. 3.

To be the invention process partial transmission sequence method count analogous diagram under the situation in out of phase to Fig. 4.

Fig. 5 is the CCDF curve of the invention process modified model iterative PTS method.

Fig. 6 is the BER curve of the invention process modified model iterative PTS method.

Embodiment

At of the requirement of next generation wireless communication system to the high quality information accuracy, at the problem and the challenge that exist in the existing OFDM wireless communication system, ofdm system model under frequency selective fading channels, complexity with the reduction traditional algorithm is a starting point, reduce on the basis of peak-to-average power than (PAPR) at traditional partial transmission sequence method (PTS), propose a kind of modified model iterative PTS algorithm.It is characterized in that comprising the following steps: that the combination that the frame OFDM symbol segmentation that will import becomes subsequence, each sub-piece addition of V non-overlapping copies to ask minimum PAPR, integration side information and selection to have minimum PAPR sends.

The described frame OFDM symbol segmentation that will import becomes the subsequence particular content of V non-overlapping copies to comprise: in comprising N sub-carrier OFDM system, transmitting data information is through the mapping of modulation systems such as QAM, data flow X _kCarry out obtaining the time domain OFDM symbol after the N point IFFT conversion, the subvector that at first a frame OFDM data vector to be sent is divided into V non-overlapping copies with the adjacent method of cutting apart, the length of each subvector is N/V, and then carrying out corresponding zero padding for each subvector after cutting apart becomes V partial transmission sequence X ^v, v=1,2 ..., V, V partial transmission sequence with gained carries out the IFFT conversion respectively then.

Described each sub-piece addition asks minimum PAPR particular content to comprise: it is x that V partial transmission sequence carries out the time-domain signal that the IFFT conversion obtains ^v, v=1,2 ..., V makes x=x ¹+ x ²+ ...+x ^vCalculate the PAPR value of primary signal this moment, be designated as PAPR _Initial, and make PAPR _PTS=PAPR _Initial, PAPR wherein _PTSBe the minimum PAPR value of setting.The combination of introducing phase rotation coefficient

b _vBe also referred to as side information (SI), remove weighting V sub-piece vector, by selecting optimum phase rotation coefficient combination with phase rotation coefficient

Make that the PAPR value that merges the back sequence is minimum.

The selected scope of phase factor set be ± 1, ± i}, and initialization b _v=1, v=1,2 ... V.Initialization v=1.Through the method for searching loop, find out the b that makes the PAPR minimum _vValue.

Described integration side information particular content comprises: in same OFDM symbol, adopt zero carrier to send side information few in number, data and side information send simultaneously, need not in addition transmitted sideband information separately, reduce the complexity of receiving terminal.

The combination that described selection has a minimum PAPR sends particular content and comprises: utilize zero subcarrier structure to comprise the partial transmission sequence of side information, construct more one used for demodulation, be fixed as 1 here, the residing position of side information is the position of zero carrier among the X.Its structural form is: P=[0, and 0 ..., 0,1, b ₁, b ₂..., b _V, 0,0 ... 0].The side information frequency-region signal P that is constructed is carried out the IFFT conversion, obtain time-domain signal p.Under the situation of the time-domain signal x of the PAPR minimum that obtains, calculate x ± p in the above, the PAPR value of signal under four kinds of situations of x ± p*i, the combination of selecting to have minimum PAPR sends.

The present invention is described further below in conjunction with drawings and Examples.

The combination that the inventive method becomes subsequence, each sub-piece addition of V non-overlapping copies to ask minimum PAPR, integration side information and selection to have minimum PAPR by the frame OFDM symbol segmentation that will import sends four steps and forms.

1, the frame OFDM symbol segmentation that will import becomes the subsequence step of V non-overlapping copies

At first set up the physical layer fundamental block diagram of ofdm system.Fig. 1 has provided the transmitting-receiving block diagram of ofdm system, and this patent is applied in this system.Carry out the framing procedure of data at transmitting terminal, constitute by preface information and data message, carry out then QAM modulation, IFFT conversion, insert Cyclic Prefix after, carry out parallel serial conversion, by the OFDM time domain data that generates is flowed conversion of signals is intermediate-freuqncy signal, sends.At receiving terminal, to carry out at first exactly synchronously and the work of channel estimating, carry out after the FFT conversion demodulating qam symbol according to the parameter of estimation, estimate the error rate.

The theory diagram of traditional partial transmission sequence method (PTS) as shown in Figure 2, this invention is to propose new method on the basis of this schematic diagram.Fig. 2 has provided the schematic diagram of partial transmission sequence method, as seen it is the subsequence (being called sub-piece again) that a frame OFDM symbol segmentation of input is become V non-overlapping copies, and multiply by different weight coefficients, the composite sequence that has minimum PAPR value by selecting suitable weight coefficient to ask for respectively each subsequence.

Suppose to comprise N subcarrier in the ofdm system that transmitting data information is through the mapping of modulation systems such as QAM, data flow X _kCarry out obtaining the time domain OFDM symbol after the N point IFFT conversion, transmit and can be expressed as:

$s\left(n\right)=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_{\mathrm{<figure-callout\; id="2"\; label="k\; e\; j"\; filenames="A20081011904400141.png,A20081011904400152.png"\; state="\{\{state\}\}">k</figure-callout>}}{e}^j{2\mathrm{\&pi;kn}/N}^{},0\&le;n\&le;N-1---\left(1\right)$

Wherein, X _kBe that N is counting of IFFT conversion through the complex signal after the constellation modulation.

Partial transmission sequence method at first is divided into a frame OFDM data vector to be sent the subvector X of V non-overlapping copies with the adjacent method of cutting apart _v, v=1,2 ..., V, the length of each subvector is N/V, then:

$X=\underset{v=1}{\overset{V}{\mathrm{\&Sigma;}}}{X}_v---\left(2\right)$

It is as follows to cut apart form:

......

V partial transmission sequence with gained carries out the IFFT conversion respectively then.

2, minimum PAPR step is asked in each sub-piece addition

The combination of introducing phase rotation coefficient

b _vBe also referred to as side information (SI), remove weighting V sub-piece vector, can get with phase rotation coefficient:

$Y=\underset{v=1}{\overset{V}{\mathrm{\&Sigma;}}}{b}_v{X}^v---\left(6\right)$

1), with V partial transmission sequence X of gained ^v, v=1,2 ..., V carries out the IFFT conversion respectively, obtains time-domain signal x ^v, v=1,2 ..., V.Make x=x ¹+ x ²+ ...+x ^vCalculate the PAPR value of primary signal this moment, be designated as PAPR _Initial, and make PAPR _PTS=PAPR _Initial

2), the selected scope of phase factor set be ± 1, ± i}, and initialization b _v=1, v=1,2 ... V.Initialization v=1.

3), change b _vValue, make b _v=-1, and x=b ₁X ¹+ b ₂X ²+ ... + b _VX ^V, calculate the PAPR value PAPR of signal at this moment _TEMPIf PAPR _TEMP＜PAPR _PTS, PAPR then _PTS=PAPR _TEMP, and keep the b of this moment _vValue.

4), continue to change b _vValue be ± i that step is with 3), keep making PAPR _PTSMinimum b _vValue, and in the subsequent algorithm processing procedure, remain unchanged.

5), if v＜V, then make v=v+1, jump to step 3), up to having traveled through all b _v, v=1,2 ..., V, end loop.

Fig. 3 is complementary cumulative distribution function (CCDF) curve chart of conventional P TS method peak-to-average force ratio under partial transmission sequence number V=1,2,4,8 situations, and Fig. 4 is the CCDF curve chart of peak-to-average force ratio under the out of phase range of choice situation.As seen from the figure along with the increase of partial transmission sequence number and phase place range of choice, peak-to-average force ratio to improve characteristic just good more, but the number of times of the IFFT of required calculating also just increases, the complexity of PTS-OFDM system is also just high more.

3, integrate the side information step

In same OFDM symbol, adopt zero carrier to send side information few in number, data and side information send simultaneously, need not in addition transmitted sideband information separately, reduce the complexity of receiving terminal.

4, the combination of selecting to have minimum PAPR sends

Utilize zero subcarrier structure to comprise the partial transmission sequence of side information, construct one more and separate timing usefulness for the back, be fixed as 1 here, the residing position of side information is the position of zero carrier among the X.Its structural form is: P=[0, and 0 ..., 0,1, b ₁, b ₂..., b _V, 0,0 ... 0].The side information frequency-region signal P that is constructed is carried out the IFFT conversion, obtain time-domain signal p.Under the situation of the time-domain signal x of the PAPR minimum that obtains, calculate x ± p in the above, the PAPR value of signal under four kinds of situations of x ± p*i, the combination of selecting to have minimum PAPR sends.

The sequence that sends mainly comprises following components: X ^v, v=1,2 ..., V and the subsequence P that forms by side information, wherein original message to be sent is: X=X ¹+ X ²+ ... + X ^VThe transmission information that needs after this method becomes: X _PTS=b ₁X ^V+ b ₂X ^V+ ... + b _VX ^V+ P.

The effect of fix information 1 is the phase place rotation that is used for judging side information among the P.Separate timing at receiving terminal, carry out the FFT conversion earlier, take out side information then, again data message is handled behind the judgement side information, solved the problem that side information sends.

Fig. 5 is the CCDF curve of conventional P TS algorithm and modified model iterative PTS algorithm, and Fig. 6 is the iterative PTS algorithm (being side information 100% errorless transmission) that do not contain side information and the BER curve of modified model iterative PTS algorithm.This method has guaranteed the reliability of system when reducing algorithm complex as seen from the figure.

In the ofdm system model of the present invention under frequency selective fading channels, complexity with the reduction traditional algorithm is a starting point, partial transmission sequence method (PTS) in traditional signal scrambling code class technology reduces on the basis of peak-to-average power than (PAPR), propose a kind of modified model iterative PTS algorithm, greatly reduce the complexity of system and need not other transmitted sideband information.

Claims (1)

1, the iterative PTS method of modified model reduction peak-to-average force ratio in a kind of ofdm system, it is characterized in that: the ofdm system model under frequency selective fading channels, reduce at traditional partial transmission sequence method on the basis of peak-to-average power ratio, propose a kind of modified model iterative PTS algorithm, comprise the following steps: that the combination that the frame OFDM symbol segmentation that will import becomes subsequence, each sub-piece addition of V non-overlapping copies to ask minimum PAPR, integration side information and selection to have minimum PAPR sends;

Become the subsequence particular content of V non-overlapping copies to comprise a frame OFDM symbol segmentation of input: in comprising N sub-carrier OFDM system, transmitting data information is through the mapping of modulation systems such as QAM, data flow X _kCarry out obtaining the time domain OFDM symbol after the N point IFFT conversion, at first a frame OFDM data vector to be sent is divided into V little overlapping subvector mutually with the adjacent method of cutting apart, the length of each subvector is N/V, and then carrying out corresponding zero padding for each subvector after cutting apart becomes V partial transmission sequence X ^v, v=1,2 ..., V, V partial transmission sequence with gained carries out the IFFT conversion respectively then;

Each sub-piece addition asks minimum PAPR particular content to comprise: it is x that V partial transmission sequence carries out the time-domain signal that the IFFT conversion obtains ^v, v=1,2 ..., make x=x ¹+ x ²+ ...+x ^vCalculate the PAPR value of primary signal this moment, be designated as PAPR _Initial, and make PAPR _PTS=PAPR _Initial, PAPR wherein _PTSBe the minimum PAPR value of setting, introduce the phase rotation coefficient combination b _vBe also referred to as side information (SI), remove weighting V sub-piece vector,, make that the PAPR value that merges the back sequence is minimum by selecting optimum phase rotation coefficient combination with phase rotation coefficient, the phase factor set select scope be ± 1, ± i}, and initialization b _v=1, v=1,2 ... V, initialization v=1 through the method for searching loop, finds out the b that makes the PAPR minimum _vValue;

Integrating the side information particular content comprises: in same OFDM symbol, adopt zero carrier to send side information few in number, data and side information send simultaneously, need not in addition transmitted sideband information separately, reduce the complexity of receiving terminal;

The combination that selection has a minimum PAPR sends particular content and comprises: utilize zero subcarrier structure to comprise the partial transmission sequence of side information, one of many structure are used for demodulation, here be fixed as 1, the residing position of side information is the position of zero carrier among the X, and its structural form is: P=[0,0, ..., 0,1, b ₁, b ₂..., b _V, 0,0 ... 0], the side information frequency-region signal P that is constructed is carried out the IFFT conversion, obtain time-domain signal p, under the situation of the time-domain signal x of the PAPR minimum that obtains in the above, calculate x ± p, the PAPR value of signal under four kinds of situations of x ± p*i, the combination of selecting to have minimum PAPR sends.

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